Outline

Foramen magnum decompression (FMD) has been proposed as the first choice treatment of foraminal syringomyelia (FS). However, a subtype of patients has demonstrated no benefit from this surgical procedure.

In our Department from January 1980 to February 2007 eighty-three consecutive patients underwent FMD for FS. In 1988 Filizzolo et al. compared FMD versus terminal ventriculostomy for treatment of FS: they reported 70% favourable results after FMD without obex plugging and only 30% after terminal ventriculostomy; additionally, in this series 13% of patients worsened after FMD. Based on the etiopathogenetic hypothesis described by Aboulker and Ball and on the cine-MRI studies performed by Oldfield, it is clear that an existing differential pressure proximal and distal to the cranio-spinal junction is responsible for syringomyelia formation and can be due to a number of pathological condition other than Chiari malformation (e.g. cranio-spinal junction malformations, spondyloarthrosis of high cervical vertebrae, kyphoscoliosis, arachnoiditis). These pathological conditions are hardly curable via FMD. Additionally, the natural history of patients affected by FS is variable and an early diagnosis favourably affects the results after surgery.

Based on these considerations, in 1993 Versari et al. presented a series of 40 consecutive patients where FMD results were analyzed retrospectively recording preoperative patient data (clinical evolution, neurological impairment and radiological features). On the basis of the score, four grades of gravity were established. All grades I and II had benefit from surgery, most grades III had favourable results from FMD; conversely, all grades IV had worsening of clinical condition postoperatively. The overall results of this series showed improvement after surgery in 63% of patients, 22% unchanged and 15% worsened (2 grade III patients and 4 grade IV patients).

To improve selection of patients for FMD and ameliorate outcomes after surgery, we have been applying this grading system prospectively since 1990. Grade IV patients are being excluded from surgical elective procedure of FMD. Forty-three patients have been enrolled in this study (30 females, 13 males, mean age 36 years, range 1-64 years, 3 grade I patients, 28 grade II patients, 12 grade III patients). Long-term results of this prospective series are as follow: improvement in 100% of grade I patients, improvement in 70% of grade II patients and 55% in grade III patients. Overall results show 70% improved patients, 28% unchanged and only 2% worsened (1 grade III patient). Mortality rate was 0%.

The Authors conclude that a better selection of patients for FMD via the application of this grading system allow decreasing of unfavourable results from 15% to 2%.